Cells, the fundamental unit of life
(Editor’s note: This is the second segment in a three-part series on viruses planned for publication.)
This week, I’m not going to go into SARS CoV-2, the virus that causes COVID; I think we’ve all heard enough about COVID recently. Instead, this week, we are going to drill down about the basics of life: how we work at the cellular level, and how we differ from viruses.
All living things are made of cells, cells were first observed in the 17th century immediately after the invention of the microscope by a Dutch scientist, Antonie van Leeuwenhoek; an English contemporary, Robert Hooke first coined the term cell shortly following. In the early 19th century, the now universally accepted Cell Theory was established, which in its present interpretation states: energy flow occurs within cells, heredity information (DNA) is passed on from cell to cell, and all cells have the same basic chemical composition.
In eukaryotic cells (all living things except for the bacteria), each cell is composed of a cellular membrane that encloses the structure and isolates the inner parts of the cell from the outside world. The cellular membrane is a thin lipid (fat) layer, with embedded proteins interspersed throughout. Inside the cell, there are a number of smaller, organized structures, called organelles that carry out the functions of the cell.
One of these organelles, the mitochondria, carry out cellular metabolism – harvesting the energy stored in the chemical bonds of sugars, producing CO2 in the process. Others are sites where proteins are manufactured from their amino acid building blocks. Still another is the nucleus, which contains the instructions for all the cellular functions; encoded in a chemical known as DNA.
DNA is a long, linear molecule; its length much longer than the cell itself, in the nucleus of the cell, it is coiled in discrete bundles we call chromosomes. The instructions are used to create a working copy composed in a different chemical compound, RNA – which carries out the execution of a cell’s work. Sexual reproduction is the risky business of halving our chromosome compliment and combining them with half of someone else’s and watching how it turns out.
Although some cells are very highly specialized and highly modified, most cells share a pretty similar architectural design. They have an external lipid membrane, and a variety of internal structures, the organelles. The master plan for the functionality of each cell is encoded in DNA, stored in the nucleus.
Viruses have a fairly similar overall design – only much, much simpler. They have an outer shell, called a viral envelope. Inside the viral envelope, there are usually no, or at least very few organized substructures. They have a small stand of DNA, and some viruses only have RNA inside the viral envelope. When they infect a cell, they commandeer the organelles of the host cell to manufacture new viral particles, using the instructions encoded in the viral DNA or RNA.
While you are sheltering, washing your hands frequently, and keeping a safe distance from others, take time to go outside and enjoy nature. Breathe fresh air, get some exercise and let the wonders of our natural world ease your tension and anxieties. This will pass, and we will have a better future for what we have learned.
Dr. J. Bruce Neill is the director of education for the Sanibel Sea School. Part of the Sanibel-Captiva Conservation Foundation family, its mission is to improve the ocean’s future, one person at a time.